Isolated renal brush border membrane vesicles actively transport many solutes including phosphate (Pi), D-glucose, L-amino acids and glycine. It is known that agents known to alter the renal reabsorption of Pi in vivo such as parathyroid hormone (PTH) effect parallel changes in Pi transport by isolated renal brush border vesicles. It is suspected that PTH acts through activation of renal tubular basal-lateral membrane adenyl cyclase and subsequently cyclic AMP (cAMP) dependent protein kinase known to be present in the brush border to effect brush border membrane phosphorylation and alteration of Pi transport. Brush border membranes can be autophosphorylated in vitro. We intend to: (a) effect cAMP independent and dependent autophosphorylation of brush border membrane vesicles in vitro and study the effects of phosphorylation of Pi and other solute transport by those membranes. (b) analyze the effects of in vivo administration of parathyroid hormone, 1,25 dihydroxycholecalciferol (DHCC), cAMP, or growth hormone, parathyroidectomy, and alterations in dietary Pi intake, on brush border membrane endogenous protein kinase activity with effects of the manipulations listed in b on isolated brush border membrane vesicle solute transport. In this manner we will test the hypothesis that PTH induced alterations in renal Pi or other solute transport are mediated in the manner described in the first paragraph above, and gain insight into the mechanisms by which DHCC, cAMP and growth hormone alter renal Pi reabsorption. Brush border membrane will be isolated by a calcium precipitation technique. Pi or other solute transport by the brush border membranes will be measured by a Millipore filtration technique. Brush border membrane phosphorylation will be measured by a protein kinase assay which employs trichloracetic acid (TCA) precipitation of phosphorylated membranes.